This is a request for a supplement to Grant AM 15796-O1A1 entitled "Synovial Cells and the Etiology of Rheumatoid Arthritis". At an international Symposium on "Infection and Immunology in the Rheumatic Diseases" held in London from 19-21 March 1974 the view prevailed that the etiologic agent in rheumatoid arthritis is a virus to which the host mounts an immunologic response. In organizing our most recent studies for presentation at the meeting, we formulated as our continuing objective the search for a viral agent in rheumatoid arthritis using primarily synovial cell cultures. We reviewed our capacity to meet this objective, and in this supplement note an extension and expansion of methods described earlier. A) Techniques for virus rescue: Synovia from rabbit joints injected with rheumatoid synovial cells (RSC), or the earliest cells grown out from rheumatoid membrane explants, will be serially passaged, co-cultivated or fused with several cell types. B) Immunologic techniques: several sensitive methods will be used to detect a "neoantigen" in human RSC, or in rabbit synovial cells derived from RSC-injected rabbit joints. C) Transfer of "traits" of RSC to normal cells: Enhanced hyaluronate synthesis will be used as a trait to transfer to other cells. The expanded scope of this work cannot be met with resources from the present grant, and hence a supplement is requested to provide professional support, additional technical help, and items of needed equipment and supplies.